Modulator and demodulator



Oct 27, 1936. v H. F. ELLIOTT I MODULATOR AND DEMODULATOR Filed April 27, 1932 A 1-." ll

lilll Ill 2? 4 'INVENTOR Harold 2? Elliott B'Y HlS -ATTORNEY I Patented Oct. 27, 1936 UNITED STATES PATENT OFFICE Application April 27,

12 Claims.

My invention relates to modulators and demodulators employing electron tubes, and particularly to modulators and de-modulators in which a portion of the circuits are arranged in balanced relation. Modulators and ole-modulators of the type employing two electron tubes arranged in push-pull are well-known in the communication art and their functions, advantages, etc. are described in many publications. An object of my invention is the provision of methods and circuits whereby a single electron tube having symmetrically arranged control grids may for many purposes replace the double tube systems heretofore employed. One advantage of employing a single tube is the reduction in cost of the tube equipment; another advantage of employing a single tube is the simplification of the associated circuits and the reduction in the cost thereof; another advantage of employing a single tube is the elimination of certain costly balanced transformers that have heretofore been necessary. Another advantage of using a single tube arises from the elimination of unwanted currents in the output circuit which have limited the output of systems heretofore employed. One of the objects of my invention, therefore, is'to suppress currents, which are not useful, by suitable arrangement of the grids within the tube, thereby increasing the useful output of the tube. My arrangement makes it possible to obtain considerably more output from one tube, than has heretofore been possible with two tubes of corresponding power consumption. These and other advantages of my system will be apparent from the following description and the appended claims wherein the novel features of my invention are defined.

Referring to the drawing:

Figs. 1 and 2 illustrate tubes suitable for carrying out the objects of my invention.

Fig. 3 shows a typical circuit whereby the objectives may be obtained.

Referring to Figure 1, which illustrates a tube suitable for carrying out the objects of the invention, numeral I designates the glass .envelope for the tube. Numeral 2 designates the cathode which is of the unipotential type mounted as usual within the envelope. Numeral 3 designates the connection from the lower end of the cathode, which connection may be brought out to a terminal on the base of the tube. With-'- in the cathode is the usual filament or heater wire 4 from the ends of which extend connections 5, 5 to exterior terminals, as will be under- 55 stood Numeral-t designates the ariodeyand 1932, Serial No. 607,857

numeral 1 the connection for the same brought out to a terminal on the base. Numerals 8 and 9 designate two control grids symmetrically arranged in the space between the cathode and the anode. Dotted lines are used for one grid and 1 full lines for the other in order that the construction may be shown clearly. Numerals I0 and l I designate the terminals for the two grids, also having exterior attachment through the base.

Figure 2 shows a second tube also suitable for carrying out the objects of the invention. This tube is similar to that of Figure 1 except that an additional electrode in the form of a screen grid 12 is placed between the control grids 8and 9 and the main anode 6. Terminal I3 is the external connection for screen [2.

Figure 3 shows a typical circuit suitable for performing the functions of modulation or demodulation in accordance with the principles of my invention. The electron tube I 4 preferably, though not necessarily, takes the general form of one of the tubes shown in Figs. 1 and 2. If the tube of Fig. l is employed the screen grid 12 and its associated source of potential I5, and by-pass capacitor It may be omitted. The circuits of Fig. 3 show an arrangement whereby one alternating current may'be used to modulate another alternating current. One of the currents may be supplied from circuit I! and the other from circuit l8 through any suitable method of coupling, as for example, by transformers ||-l9 and. 18-20, as shown. The two grids 8 and 9 of tube l4 may be connected to opposite terminals of secondary l9, and the latter may be provided with a tap at its electrical center. A connection may be run from this electrical center to the cathode 2 and may include transformer winding 20 and a suitable source of grid biasing potential 23 with by-pass capacitor 24. 4 The source 23 of biasing potential, may be either a battery, as shown, or any other well known means for that purpose. In this particular art, grid leaks are one of the known means for establishing a bias. Furthermore, if desired, a tuned circuit, resonant at one of the resultant frequencies may be employed in the grid circuit for the purpose of increasing the output, in accordance with disclosure in my co-pending application filed of even date herewith, S. N. 607,- '50 856. The output circuit of the tube may include an output transformer 25-26 and a suitable source of anode potentialll with by-pass capacitor 28. By suitable choice of tube constants and potentialsthe electrical characteristics of the system may be made non-linear. Alternating currents from circuits I! and. I8 will then modulate one another in tube l4, and the resultant modulated or de-modulated currents may be delivered in circuit 26. With the arrangement shown, alternating currents from circuit I! are applied to the two grids 8 and 9 in phase opposition and alternating currents from circuit l8 are applied to the two grids 8 and 9 in phase addition. With the balanced grid structure shown in Figs. 1 and 2, alternating currents which are applied to the grids in phase opposition, as from circuit I1, will not appear in substantial amount in the output circuit 26. This increases the power handling capacity of the tube for useful modulated or de-modulated currents and eliminates the costly balanced transformer which is required whentwo tubes arranged in push-pull are used to accomplish the same purpose. The relations of the various currents in the circuits may be controlled by tuning to resonance any or all of the circuits associated with the input and output, as for example, by use of capacitors 2|, 22 and 21.

The typical arrangement shown in Fig. 3 for the purpose of illustrating my invention provides for modulating one alternating current with another, as before mentioned. It will be apparent to those skilled in the art that the invention is not limited to these functions, but that the principles, as defined in the appended claims, may be applied to a great variety of other purposes, such for example, as the modulation of a direct current by an alternating current, the de-modulation of single side band signals, and the performance of many other functions in electrical communication and other arts. Any of the input or output circuits of the tube and any of the sources of potential associated therewith may be arranged for either direct currents or alternating currents or one of these may be superimposed upon the other. Any of the input or output transformers shown in Fig. 3 may be replaced by any system of reactors, resistors or impedances suitable for applying the desired currents and potentials to the input and output circuits. 7

What I claim is:

1. A modulator or demodulator comprising an electron tube having a cathode, an anode, and two symmetrically arranged control grids, an input circuit for applying an externally supplied fluctuating potential to the two grids in phase and another input circuit for applying another externally supplied fluctuating potential to the grids in phase opposition, means for biasing the grids, and an output circuit comprising said cathode and anode, and an impedance and a source of potential for said output circuit.

2. A modulator or demodulator comprising an electron tube having a cathode, an anode, and a plurality of intermeshed control grids, an input circuit comprising said cathode, means applying a fluctuating potential to the grids in like phase, means of applying another fluctuating potential to the grids in different phase, said potentials comprising a modulating potential and a potential to be modulated, said modulating and modulated potentials both being supplied from external sources, an energy coupling means, a source of potential, and an output circuit comprising said cathode, anode, coupling means and source of potential.

3. A modulator or demodulator comprising an electron tube having a cathode, an anode, and multiple symmetrically arranged control means cooperating therewith, means for applying a fluctuating modulating potential and a fluctuating potential to be modulated from two separate external sources, to the control means, one potential being applied to the multiple control means in like phase and the other in difiering phase, and means for deriving a selected modulated or demodulated fluctuating potential from the output.

4. A modulator or demodulator comprising an electron tube having a cathode, an anode, and two symmetrically arranged control grids, means for applying one alternating current potential to the two grids in phase opposition and another alternating current potential to the two grids in phase addition, said potentials both being derived from sources separate from the tube, means for biasing the grids relatively to the cathode, energizing means inter-connecting the cathode and anode, and means for deriving selected modulated or demodulated alternating current potentials from the cathode and anode.

5. A modulator or demodulator comprising in combination with discrete external sources of alternating potentials, an electron tube having a cathode, an anode, a screen grid, and two symmetrically arranged control grids, means for applying one of said discrete alternating potentials to the two grids in phase opposition and another of said discrete alternating potentials to the two grids in phase addition, said potentials being derived from two currents which are to be modulated or demodulated one with the other, means for biasing the control grids relatively to the cathode, energizing means inter-connecting the cathode and anode, and means for deriving selected modulated or demodulated potentials from the cathode and anode.

6. The method of modulation or demodulation which comprises applying fluctuating modulating potentials and fluctuating potentials to be modulated from two discrete sources differently to symmetrically arranged control means in an electron tube, one potential being applied in phase opposition and the other in phase addition, setting up an electron flow within the tube, and deriving selected fluctuating modulated potentials from variations in the flow.

7. A grid circuit modulator comprising in combination with discrete external sources of alternating potentials, a coplanar grid tube having intermeshed grids, means for applying one of said discrete potentials to be modulated to the grids in one phase relation, means for applying another of said discrete potentials as a modulating potential to the grids in another phase relation, said relations comprising phase opposition for one potential and phase addition for the other, means for biasing the grids, and means for deriving a selected modulated output current.

8. In combination, discrete sources of fluctuating potentials to be modulated with one another, an electron tube having a cathode, anode and two intermeshed grids, means for applying one of the potentials to the grids in opposing phase relations and the other in aiding phase relations, means biasing the grids, and means delivering desired potentials and suppressing undesired potentials in the output.

9. A modulator or demodulator comprising in combination with discrete sources of potential,

an electron tube having a cathode, an anode and 75 two equal and intermeshed control grids, a balanced input circuit comprising the grids and impedances connected serially with a tap at a point of balance relative to the cathode, a connection including at least one tuned impedance from the tap to the cathode, means for applying a modulating or demodulating potential and a potential to be modulated or demodulated from said discrete sources to the control grids in different phase relations, and means including a source of energy for deriving selected potentials from the anode and cathode.

10. A modulator or demodulator comprising a coplanar grid electron tube having intermeshed grids, an input circuit for applying a fluctuating potential from an external source to the grids in phase opposition, means applying another fluctuating potential from an external source to the grids in phase addition, and means for selectively tuning a circuit including the grids in parallel for fluctuating potentials therein.

11. In combination, a coplanar grid electron tube having intermeshed grids, a circuit for applying an external alternating potential to the grids in phase opposition, a circuit for applying a second external alternating potential to the grids in phase addition, and means resonating a circuit including the grids in series for alternating potentials therein.

12. In combination, an electron tube of the coplanar grid type having intermeshed grids, a circuit applying an external periodic potential to the grids in series, a circuit applying another external periodic potential to the grids in parallel, an output circuit, and means resonating the input and output circuits for periodic potentials therein.

HAROLD F. ELLIOTT. 

